RF drying can be used for example to dry green i.e. freshly cut wood, from high moisture content down to approaching 12% moisture content RF drying relies on the inherent properties of water within the green timber to absorb the RF energy. The water molecules are bipolar and switch polarity as the radio frequency wave passes through the water within the timber. The “switching” action of the water molecules heats the water. The resultant heat energy transfers itself through the structure of the timber thereby heating the body of the timber causing a diffusion of moisture within the timber to the surface of the timber for evaporation.
Typically RF timber drying requires a considerable amount of ‘setting up’ before the drying process can commence. When a filleted timber stack is placed in the kiln, capacitor plates are interleaved between layers of the filleted timber stack load before each capacitor plate is connected to an RF generator to commence the RF drying process. Placing capacitor plates between layers of timber is required to ensure that sufficient RF energy penetrates all of the timber. This system works well when the timber has a high moisture content and the resultant ‘load’ is large due to the large amount of moisture present in the timber and the relatively high dielectric loss factor of water. However, as the timber dries out the load decreases and the amount of RF power being delivered into the load becomes more difficult to control.
There is a need for a method and system for RF drying timber that reduces equipment set-up when a load of timber is placed in a drying chamber and/or is operable such that the RF power being delivered into the load is more controllable while the timber load is drying.
It is an object of the present invention to provide an improved RF timber drying system and method, or at least to provide the industry or the public with the useful choice.